A recent flame-sampling laser-ionization study [Chem. Phys. Lett. 275 (1997) 278] reported that combustion of dimethyl methyl phosphonate generates the elusive CH3P(=O)(2) molecule and that it has an ionization energy (IE) of 9.24 +/- 0.01 eV. Ab initio calculations (CBS-QB3 level of theory) indicate that this IE is that of the 'enol' tautomer CH2=P(=O)OH, while that of CH3P(=O)(2) is much higher, 11.66 eV. We propose that in the above experiments, a trace amount of the 'enol' is co-generated with the 'keto' isomer CH3P(=O)(2). Mass spectrometric experiments involving Neutralization-Reionization (NR) and Collision-Induced Dissociative Ionization (CIDI) show that CH2=P(=O)OH and CH3P(=O)(2) are both stable neutral species in the dilute gas-phase. (C) 2002 Elsevier Science B.V. All rights reserved.